The present invention relates to gas turbine engine casings, particularly gas turbine engine fan casings and turbine casings, more particularly to an improved blade containment assembly for use within or forming a part of the gas turbine engine casing.
Turbofan gas turbine engines for powering aircraft conventionally comprise a core engine, which drives a fan. The fan comprises a number of radially extending fan blades mounted on a fan rotor enclosed by a generally cylindrical fan casing. The core engine comprises one or more turbines, each one of which comprises a number of radially extending turbine blades enclosed by a cylindrical, or frustoconical, casing.
There is a remote possibility that with such engines that part, or all, of a fan blade, or a turbine blade, could become detached from the remainder of the fan or turbine. In the case of a fan blade becoming detached this may occur as the result of, for example, the turbofan gas turbine engine ingesting a bird or other foreign object.
The use of containment rings for turbofan gas turbine engine casings is well known. It is known to provide generally cylindrical, or frustoconical, relatively thick metallic containment rings. It is also known to provide generally cylindrical, or frustoconical, locally thickened, isogrid, metallic containment rings. Furthermore it is known to provide strong fibrous material wound around relatively thin metallic casings or around the above mentioned containment casings. In the event that a blade becomes detached it passes through the casing and is contained by the fibrous material.
However, the relatively thick containment casings are relatively heavy, the relatively thin casings enclosed by the fibrous material are lighter but are more expensive to manufacture. The relatively thick casings with fibrous material are both heavier and more expensive to manufacture.
Accordingly the present invention seeks to provide a novel gas turbine engine casing which overcomes the above mentioned problems.
Accordingly the present invention provides a gas turbine engine rotor blade containment assembly comprising a generally cylindrical, or frustoconical, casing arranged in operation coaxially around a rotor carrying a plurality of rotor blades, the casing having an upstream portion upstream of a plane containing the most upstream point of the leading edge of the rotor blades, the casing having a containment portion downstream of the plane containing the most upstream point of the leading edge of the rotor blades, at least a part of the containment portion of the casing having a greater diameter than the diameter of the upstream portion of the casing, the containment portion having a zone substantially in the plane of the leading edge of the tips of the rotor blades, the containment portion of the casing having a maximum diameter in the zone substantially in the plane of the leading edge of the tips of the rotor blades to restrain upstream movement of a detached rotor blade.
Preferably the containment portion progressively increases in diameter from the upstream portion of the casing to the zone substantially in the plane of the leading edge of the tips of the rotor blades and the containment portion progressively increases in diameter from a plane containing or downstream of the trailing edges of the road for blades to form a substantially radially outwardly dished shape in the casing.
Preferably the casing comprises an annular member positioned axially upstream of the tip of the rotor blade, the annular member extending in a radially inwardly direction from the metal casing, the containment portion being downstream of the annular member, the containment portion of the casing having a greater diameter than the diameter of the casing at the annular hook.
Preferably the annular member is substantially in the plane containing the most upstream point of the leading edge of the rotor blades.
Preferably the annular member is an annular hook extending in a radially inwardly and axially downstream direction from the casing towards the tips of the rotor blades.
Preferably the containment portion of the casing is thicker than the remainder of the casing.
Preferably the containment portion comprises one or more curved lines in axial cross-section.
Alternatively the containment portion comprises one or more straight lines in axial cross-section.
Preferably the containment portion comprises at least one circumferentially extending rib.
Preferably a rib is arranged substantially in or adjacent the plane containing the leading edge of the tips of the rotor blades. Preferably a rib is arranged substantially in a plane containing the mid-chord of the rotor blades. Preferably a rib is arranged substantially in a plane upstream of the trailing edges of the rotor blades.
Preferably the rotor blade is a forwardly swept rotor blade.
Preferably the casing is a fan casing and the rotor blades are fan blades.
Alternatively the casing is a turbine casing and the rotor blades are turbine blades.
Preferably the casing is formed from a metal, for example titanium, an alloy of titanium, aluminium, an alloy of aluminium or steel.
The present invention also provides a gas turbine engine comprising a rotor carrying a plurality of rotor blades, a rotor blade containment assembly comprising a generally cylindrical, or frustoconical, casing arranged coaxially around the rotor and rotor blades, the casing having an upstream portion upstream of a plane containing the most upstream point of the leading edge of the rotor blades, the casing having a containment portion downstream of the plane containing the most upstream point of the leading edge of the rotor blades, at least a part of the containment portion of the casing having a greater diameter than the diameter of the upstream portion of the casing, the containment portion having a zone substantially in the plane of the leading edge of the tips of the rotor blades, the containment portion of the casing having a maximum diameter in the zone substantially in the plane of the leading edge of the tips of the rotor blades to restrain upstream movement of a detached rotor blade.